In recent years, fat mass is gaining attention as an indicator used to determine the health of a measurement subject. In particular, visceral fat mass is gaining attention as an indicator for determining whether or not a person is suffering from central obesity. Central obesity is said to bring about lifestyle-related diseases that can easily lead to artery hardening, such as diabetes, hypertension, and hyperlipidemia, and the stated indicators hold promise in terms of preventing such diseases. “Visceral fat” refers to fat that accumulates around the internal organs on the inner side of the abdominal muscles and the back muscles, and is distinct from the subcutaneous fat that is located toward the surface of the trunk area. It is typical to employ the area occupied by visceral fat in a cross-section of the trunk area that corresponds to the navel (referred to as a “visceral fat cross-sectional area” hereinafter) as an indicator of the visceral fat mass.
Normally, visceral fat mass is measured by analyzing images obtained through X-ray computed tomography (CT), magnetic resonance imaging (MRI), or the like. In such image analysis, the visceral fat cross-sectional area is calculated geometrically from a tomographic image of the trunk area obtained by using X-ray CT, MRI, or the like. However, it is necessary to use several pieces of large equipment installed in a medical facility, such as X-ray CT, MRI, or other machines, in order to make use of such a measurement method; thus it is extremely difficult to measure visceral fat mass on a daily basis through such a measurement method. X-ray CT also poses the problem of exposure to radiation, and thus cannot necessarily be called a desirable measurement method.
A body impedance technique is being considered as an alternative to these measurement methods. For example, JP 2002-369806A discloses a body fat measurement device configured having electrodes provided on the inner circumferential surface of a belt member, where the belt member is wrapped around and anchored to the trunk area of a measurement subject so that the electrodes are placed in contact with the trunk area; a body impedance is measured using the electrodes that have been placed in contact with the trunk area, and body fat mass, such as visceral fat mass and subcutaneous fat mass, can then be calculated based on the measured body impedance.
Meanwhile, to make it possible to measure the visceral fat mass, subcutaneous fat mass, and so on with a high degree of accuracy using the stated body impedance, it is necessary to take actual measurements of the measurement subject's body build, such as the circumferential length of the trunk area, the trunk area width, and the trunk area depth, and use the measurements in computational processes for calculating the body fat mass. JP 2005-288023A, JP 2008-23232A, JP 2008-237571A, JP 2009-22482A, and so on have been disclosed as body fat measurement devices that operate from such a standpoint, by taking actual measurements of the measurement subject's trunk area width, trunk area depth, and so on during measurement and using those measurements in computational processes for calculating the body fat mass.
The stated JP 2005-288023A discloses a body fat measurement device configured so that a fitting unit that is fitted to a measurement subject's abdominal area is provided upon a pair of arm portions, which make contact with both sides of the measurement subject's trunk area (in other words, both flanks), so that the fitting unit is mobile; the trunk area width is measured by bringing the arm portions into contact with both flanks.
The stated JP 2008-23232A discloses a body fat measurement device configured so that a fitting unit that is fitted to a measurement subject's abdominal area is provided upon an arm portion, which makes contact with the measurement subject's back, so that the fitting unit is mobile; the trunk area depth is measured by bringing the arm portion into contact with the back.
The stated JP 2008-237571A discloses a body fat measurement device configured so that a trunk area width measurement unit disposed at a distance from the outside of both sides of a measurement subject's trunk area is separate from a fitting unit fitted to the measurement subject's abdominal area; the configuration is such that multiple non-contact range sensors are provided in the trunk area width measurement unit in order to take an actual measurement of the trunk area width.
Furthermore, the stated JP 2009-22482A discloses a body fat measurement device that, instead of placing electrodes in contact with a measurement subject's trunk area, provides foot electrodes on a platform unit onto which the measurement subject steps; a trunk area width measurement unit disposed at a distance from the outside of both sides of the measurement subject's trunk area is supported on a support column portion that extends upward from the stated platform unit while the measurement subject stands on the platform unit, and multiple non-contact range sensors are provided in the trunk area width measurement unit so as to take an actual measurement of the trunk area width.
In addition, although not discussing a specific device configuration, JP 2008-228890A mentions being able to accurately measure visceral fat mass and subcutaneous fat mass by placing electrodes in contact with the back of a measurement subject's trunk area (that is, the back) without placing electrodes in contact with the measurement subject's abdominal area and placing electrodes in contact with the hands and feet of the measurement subject, measuring the body impedance, and calculating the visceral fat mass and the subcutaneous fat mass based on the measured body impedance. One of the reasons for this is that the subcutaneous fat that accumulates on the abdominal area side is relatively thinner than the subcutaneous fat that accumulates on the back area side, and thus if the electrodes are placed in contact with the abdominal area, the current that is applied will flow through fat-free areas, which makes it easy for errors to occur.